文字列の 2, 7, 12, 17, 22 文字目をアンマネージメモリ上で変更して新たに文字列を作成する

string_pointer_test.cs

using System;
using System.Runtime.InteropServices;

class Program
{
    static void Main(string[] args)
    {
        string str = "ABCDEabcde01234ひらがなカタカナ漢字", newstr1, newstr2;

        IntPtr ptr = Marshal.StringToHGlobalUni(str);
        Marshal.WriteInt16(IntPtr.Add(ptr, sizeof(short) *  2), (short)'-');
        Marshal.WriteInt16(IntPtr.Add(ptr, sizeof(short) *  7), (short)'-');
        Marshal.WriteInt16(IntPtr.Add(ptr, sizeof(short) * 12), (short)'-');
        Marshal.WriteInt16(IntPtr.Add(ptr, sizeof(short) * 17), (short)'-');
        Marshal.WriteInt16(IntPtr.Add(ptr, sizeof(short) * 22), (short)'-');
        newstr1 = Marshal.PtrToStringUni(ptr);
        Marshal.FreeHGlobal(ptr);

        unsafe
        {
            fixed (char* p = str.ToCharArray())
            {
                p[ 2] = '-';
                p[ 7] = '-';
                p[12] = '-';
                p[17] = '-';
                p[22] = '-';
                newstr2 = new string(p);
            }
        }

        Console.WriteLine(str);
        Console.WriteLine(newstr1);
        Console.WriteLine(newstr2);
    }
}